The present invention generally relates to linear travel measurement devices.
In the control of fluid in industrial processes, such as oil and gas pipeline systems, chemical processes, etc., it is often necessary to reduce and control the pressure of a fluid. Regulators are typically used for these tasks by providing adjustable flow restriction through the regulator. The purpose of the regulator in a given application may be to control flow rate or other process variables, but the restriction inherently induces a pressure reduction as a by-product of its flow control function.
By way of example, a specific application in which regulators are used is the distribution and transmission of natural gas. A natural gas distribution system typically includes a piping network extending from a natural gas field to one or more consumers. In order to transfer large volumes of gas, the gas is compressed to an elevated pressure. As the gas nears the distribution grid and, ultimately, the consumers, the pressure of the gas is reduced at pressure reducing stations. The pressure reducing stations typically use regulators to reduce gas pressure.
It is important for natural gas distribution systems to be capable of providing sufficient volumes of gas to the consumers. The capacity of this system is typically determined by the system pressure, piping size, and the regulators, and system capacity is often evaluated using a simulation model. The accuracy of the system model is determined using flow data at various input points, pressure reducing points, and output points. The pressure reducing points significantly impact the capacity of the gas distribution system, and therefore it is important for the system model to accurately simulate the pressure reducing points. The pressure reducing points, however, are within the distribution system and therefore are not considered custody transfer points (i.e., points at which the control of gas flow switches from the distribution system to the consumer). As a result, flow measurement is typically not provided at the pressure reducing points. Furthermore, since the pressure reducing points are not custody transfer points, the added cost of high accuracy is not required. Flow measurement problems similar to those described above with respect to natural gas distribution are also present in other regulator applications (i.e., industrial processes, chemical processes, etc.).
In addition, regulators are subject to failure due to wear during operation, thereby reducing the ability to control pressure along a pipeline. A damaged regulator may allow fluid to leak, thereby increasing fluid waste and possibly creating a hazardous situation. While damaged regulators may be repaired or replaced, it is often difficult to detect when a regulator has failed and determine which regulator is damaged. Detecting a failure and determining which regulator has failed is more difficult in a typical natural gas delivery system, where pipelines may run several miles. Accordingly, apparatus which detects apparatus failure and identifies the location of the failure is greatly desired.
Linear travel measurement apparatus is often provided with equipment having moving members, such as a regulator with a throttling element, to provide feedback regarding operating parameters. In particular, field effect sensors are often used to provide information as to the position of the throttling element. Field effect sensors typically include a magnet and a magnetic field sensor which move relative to each other according to the position of the throttling element. The magnet creates a magnetic flux pattern which is sensed by the magnetic field sensor. As a result, changes in magnetic flux detected by the sensor can be used to infer the position of the magnet, and hence the throttling element. The magnet must be kept at the same longitudinal distance and attitude with respect to the sensor, otherwise the magnetic flux pattern generated by the magnetic will be altered and the linear travel feedback will be distorted and inaccurate.
In accordance with certain aspects of the present invention, a pressure regulator is provided comprising a main housing having an inlet and an outlet, a fluid flow path being defined between the inlet and the outlet, a throttling element moveable in the fluid flow path, and a throttling element position sensor. The throttling element position sensor includes a magnet housing supported in fixed relation to the main housing and defining an inner surface. A magnet is provided sized for insertion into the magnet housing and adapted for movement with the throttling element, the magnet having a north pole and a south pole, wherein the magnet generates a magnetic flux. A centering ring is positioned between the magnet and the magnet housing, the centering ring including a biased wall acting to center the magnet in the magnet housing. A magnetic field sensor is positioned to detect the magnet flux.
In accordance with additional aspects of the present invention, a magnet assembly is for use with a magnetic flux sensor to provide a position sensor adapted to detect a position of a moveable member. The magnet assembly comprises a magnet housing defining an inner surface, and a magnet sized for insertion into the magnet housing and adapted for movement with the moveable member, the magnet having a north pole and a south pole, wherein the magnet generates a magnetic flux. A centering ring is positioned between the magnet and the magnet housing, the centering ring including a biased wall acting to center the magnet in the magnet housing.